Vacuum-assisted stereotactic fixation system with patient-activated switch

ABSTRACT

A stereotactic fixation apparatus provides for accurate and reproducible positioning of a patient&#39;s skull during medical diagnostic and treatment procedures. The stereotactic fixation apparatus includes a mouthpiece having an acrylic impression formed as an impression of the patient&#39;s upper teeth and hard palate. The mouthpiece is connected to a stereotactic frame, which in turn is releasable connected to an adaptor board on which the patient rests. Vacuum pressure is used to draw the acrylic impression firmly against the patient&#39;s hard palate. Vacuum pressure is also used to hold the stereotactic frame on the adaptor board. The stereotactic fixation apparatus additionally includes a patient-activated safety release mechanism which allows the patient to disconnect the vacuum pressure and to dislodge the restraints of the mouthpiece and frame, as well as to disable the medical equipment used with the medical diagnostic or treatment procedure. A calibration phantom desirably is used with the stereotactic fixation apparatus to calibrate the orientation of the mouthpiece relative to the reference axes of the medical treatment device during each stage of the patient&#39;s course.

RELATED CASE

The present application is a continuation-in-part of application, Ser.No. 08/148,213, filed Nov. 2, 1993, now U.S. Pat. No. 5,464,411.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for immobilizing a patient'sskull during a medical diagnostic or treatment procedure, and moreparticularly to a stereotactic fixation system which permits precise andreproducible positioning of the patient's skull for focal irradiation orlike medical procedures.

2. Description of Related Art

Modern methods of imaging, such as computerized tomography and magneticresonance imaging, enable radiation oncologist to precisely delineatevolumes of diseased tissue and normal anatomical structures. The datafrom imaging scans makes it possible to tailor radiation doses to aparticular, identifiable treatment volume.

Focal radiation treatment usually involves the use of external beams,such as, for example, photon or proton beams. Such treatment requiresaccurate positioning and immobilization of the patient because a smallmisalignment in a patient's position with respect to the external beamcan result in missing the target and/or delivering the high dose ofradiation to normal, non-targeted tissue. The distance from thehigh-dose region of the external beam to its lateral and distal edges isoften but millimeters.

Radiation treatment and pretreatment diagnostic studies also requirereproducible positioning of the patient. Radiotherapy typically involvesseveral diagnostic, planning and treatment stages. At each stagesubsequent to the initial, accurate repositioning of the patient isessential. Most patients also require multiple treatments extending overseveral weeks. Variation of the treatment position between differentsessions will decrease the efficacy of the treatment.

In an effort to provide accurate and reproducible positioning of apatient, stereotactic location devices have been developed. Thesedevices rely on the assumption that the skull and its contents arerigid. Each anatomic point within the skull can then be uniquelyidentified when one knows the three spacial coordinates of that anatomicpoint.

Original neurosurgical and radiosurgical stereotactic location devicestypically attach to the patient's skull by three or four pins surgicallyaffixed. These invasive devices cannot be removed between diagnosticstudies and treatment procedures, which therefore have to be performedwithin one day.

More recently, a relocatable stereotactic location device has beendeveloped which employs a halo-ring which is invasively attached to thepatient's skull and remains in place for several weeks unless thetreatment is finished. An example of these devices is described inClark, B. G., et al., "A Halo-Ring Technique for FractionatedStereotactic Radiotherapy," The British Journal of Radiation, pp.522-527 (June 1993). Such devices, however, are still invasive and maycause discomfort to the patient.

Another prior relocatable stereotactic device is described in Delannes,M., et al., "The Laitinen Stereoadaptor," Neurochirurgie, 1990,36:167-175. This device can be quickly positioned on the patient's headusing two ear plugs and a nasal support to locate the device on theskull. However, because these fixation points contact relatively softtissue, such device inherently lacks the rigidity and reproducibility ofbony or dental fixation.

Another prior stereotactic device has also used the upper teeth oralveolar ridge to position the stereotactic device on the patient'sskull. The rigid connection between the upper teeth and the skull makethe upper teeth a convenient and non-invasive reference point of theskull. This stereotactic device is disclosed in U.K. Patent Publication2 213 066. Straps or similar structure are used in these devices tosecure a mouthpiece of the stereotactic device within the patient'smouth. These straps, however, are awkward and time consuming to use, andcan contribute to misalignment in head position. In addition, suchstraps cannot be easily and immediately removed in exigentcircumstances. For instance, in cases where the patient chokes, vomits,or otherwise has trouble breathing, the mouthpiece cannot be quicklyremoved either by the health care provider or by the patient. Inaddition, a health care provider also may not immediately recognize thepatient's condition because the stereotactic location device hasimmobilized the patient's head, and the patient may be unable to alertthe health care provider of his or her condition.

Another disadvantage of using straps is that they may be variablylocated in the radiation treatment field, thus compromising the qualityand reproducibility of dose delivery, especially where chargedparticles, such as protons, are used.

As noted above, the diagnostic, planning and treatment stages typicallyoccur over the course of several secessions and involve the use of avariety of different imaging and radiation equipment. In collaborativeprograms between different institutions, the initial planning procedurestypically occur at a facility different from that where the treatmentprocedures take place. These programs will become increasingly importantbecause only a limited number of hospitals in the United States performfocal radiation therapy.

The orientation of the stereotactic fixation device relative to thereference axes of the scanning planes of the various diagnostic andtreatment equipment used throughout the patient's course usuallydiffers. Thus, even though the same fixation apparatus may be attachedto the patient's skull during both the diagnostic and treatment stages,the patient's position with respect to the reference axes of thetreatment equipment is not exactly replicated as planned.

SUMMARY OF THE INVENTION

In view of the foregoing drawbacks and shortcomings of the priorstereotactic location devices, a need exists for a stereotactic locationdevice which is noninvasive, provides sufficient immobilization, allowsaccurate re-positioning, is well tolerated by a patient, is quicklyreleased and does not interfere with the medical procedure (e.g.,interfere with an external beam in radiotherapy). A need also exists fora way of easily calibrating the orientation of stereotactic locationdevice relative to the reference axes of various diagnostic andtreatment equipment at one or more facilities.

In accordance with one aspect of the present invention, a stereotacticfixation apparatus comprises a mouthpiece attached to a stereotacticframe. The mouthpiece has a surface that contacts the patient's hardpalate and upper teeth, and also has a port adapted for connection to asource of vacuum. Additionally, the mouthpiece is configured to providea fluidic path between the surface and the port. In the preferredembodiment, the surface of the mouthpiece is shaped to conform to thehard palate and upper teeth of the patient and has at least one holethat communicates with the port. A normally closed, one-way flow valvemay be positioned in the fluidic path between the hole and the port.Additionally, the apparatus preferably includes a vacuum control systemwhich regulates the vacuum and a patient-activated switch forterminating vacuum pressure in the fluidic path.

A further aspect of the present invention relates to a stereotacticfixation apparatus that comprises a platform for supporting the body ofa patient. A stereotactic immobilization device, such as a stereotacticframe, contacts the platform at least at one interface region. A port,connected to a source of vacuum, is in fluidic communication with theinterface region. When a vacuum pressure is applied to the interfaceregion through the port, the vacuum holds the stereotacticimmobilization device against the platform. Preferably, theabove-mentioned patient-actuated switch serves to terminate vacuumpressure not only to the mouthpiece, but also to the stereotacticimmobilization device.

According to another aspect of the invention, a method of accurately andreproducibly positioning a patient's skull for a medical procedureinvolves the use of a mouthpiece attached to a stereotactic frame. Themouthpiece is positioned within the patient's mouth so as to extendbeneath the patient's hard palate. A vacuum is applied to draw themouthpiece against the patient's hard palate and upper teeth so as tosecure the mouthpiece within the patient's mouth.

Yet another aspect of the invention comprises a method of manufacturinga mouthpiece for a stereotactic fixation apparatus. A dental impressionof a patient's teeth is made using a first material, and a study cast ofthe patient's teeth is made using the dental impression. An impressionof the study cast is then made using a second material different fromthe first material to provide a device that precisely matches thepatient's palatal and dental anatomy. A passageway is formed through themouthpiece to provide a path for drawing the mouthpiece against theinterior of the patient's mouth.

An additional aspect of the invention comprises a coupling that couplesa stereotactic frame to a mouthpiece. The coupling is configured toprovide at least three degrees of rotational movement of the mouthpiecerelative to the stereotactic frame and at least two degrees of linearmovement of the mouthpiece relative to the stereotactic frame.

In accordance with another aspect of the present invention, acalibration phantom is used to replicate the position of a stereotacticimmobilization device relative to a scanning plane of a medical device.The scanning plane has a pair of intersecting axes for referencepurposes. The stereotactic immobilization device releasably attaches toat least one point on a support apparatus used with the medical device.The calibration phantom comprises a plurality of markers located in aplane. The markers define at least two intersecting axes. A support iscoupled to the markers and is configured to releasably attach to thesupport apparatus at the same point on the support apparatus that thestereotactic immobilization device is releasably attached.

A further aspect of the invention relates to a stereotactic fixationsystem which comprises a stereotactic frame. The frame includes anattachment point. A skull immobilization device includes a firstadjustable coupling which is adapted to releasably attach to theattachment point of the frame. A calibration phantom also comprises anadjustable coupling and a plurality of markers coupled to the coupling.The markers are located in one plane and defines at least twoperpendicular axes. The adjustable coupling is adapted to releasablyattach to the attachment point of the frame.

In accordance with a preferred method of calibrating the orientation ofreference axes of a scanning plane of a first medical device relative tothe position of a detachable fixation device, with the orientation ofreference axes of a reference plane of a second medical device relativeto the same detachable fixation device, a calibration phantom isprovided. The calibration phantom has a plurality of markers that definea pair of perpendicular axes within a plane. The calibration phantom isattached to a first support apparatus used with the first medical deviceat a location where the detachable fixation apparatus is attached to thefirst support apparatus. The detachable fixation device is used toimmobilize a patient's skull. The markers of the calibration phantom arealigned with the reference axes of the scanning plane such that the axesdefined by the markers are parallel with the reference axes of thescanning plane in an aligned position. The calibration phantom then isfixed in this aligned position. After detaching the calibration phantomfrom the first support apparatus of the first medical device, thecalibration phantom later is attached to a second support apparatus usedwith the second medical device. The calibration phantom is attached tothe support apparatus at a location where the detachable fixationapparatus is attached. The second support apparatus is moved to aposition where the markers of the calibration phantom align with thereference axes of the second medical device such that the axes definedby the markers coincide with the reference axes of the second medicaldevice. In this manner, the reference axes of the scanning planes of thefirst and second devices are calibrated.

An additional aspect of the invention comprises a stereotactic fixationsystem for immobilizing a patient's skull during a medical procedureinvolving a medical device. The system comprises a platform forsupporting a portion of a patient. A stereotactic fixation apparatuscontacts the platform at least at one interface region, and a port,which is adapted for connection to a source of vacuum, is positioned influidic communication with the interface region between the platform andstereotactic fixation apparatus. The applied vacuum holds thestereotactic fixation apparatus against the platform when vacuumpressure is applied to the interface region through the port. A firstsensor is positioned proximate to the interface region, and generates afirst input signal which indicates the application or absence of avacuum at the interface region. The system also includes apatient-activated switch which has at least first and second operationalstates. The switch generates a second input signal when the switch is inone of the states. A controller receives the first and second inputsignals from the first sensor and the patient-activated switch,respectively. The controller generates an output signal when the vacuumpressure is applied at the interface region and the patient-activatedswitch is in the first state. The output signal enables the operation ofthe medical device.

A preferred method of interlocking the operation of a medical devicewith the operational state of a quick-release stereotactic fixationapparatus used to immobilize a patient's skull involves sensing thepressure at an interface region between a portion of the stereotacticfixation apparatus and a platform which supports at least the patient'sskull. From the sensed pressure, it is determined whether a vacuum isapplied at the interface region to hold the stereotactic fixationapparatus against the platform is determined. It also is determinedwhether a patient-activated switch is in a selected state. When a vacuumis applied at the interface region and the patient-activated switch isin the selected state, a signal which enables the medical device isgenerated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will now be described withreference to the drawings of a preferred embodiment which is intended toillustrate and not to limit the invention, and in which:

FIG. 1 is a top perspective view a vacuum-assisted stereotactic fixationapparatus in accordance with one preferred embodiment of the presentinvention;

FIG. 2 is a schematic front elevational view of the stereotacticfixation apparatus of FIG. 1;

FIG. 3 is an exploded top perspective view of the stereotactic fixationapparatus of FIG. 1;

FIG. 4 is a cross-sectional view of a footing of a stereotactic frametaken along line 4--4 of FIG. 1;

FIG. 5a is a schematic top plan view of the stereotactic fixationapparatus of FIG. 1 with the stereotactic frame in a first treatmentposition;

FIG. 5b is a schematic top plan view of the stereotactic fixationapparatus of FIG. 1 with the stereotactic frame in a second treatmentposition;

FIG. 5c is a schematic top plan view of the stereotactic fixationapparatus of FIG. 1 with the stereotactic frame in a third treatmentposition;

FIG. 6 is a front elevational view of a mouthpiece/coupling assemblyattached to the stereotactic frame of FIG. 1;

FIG. 7 is a side elevational view of the stereotactic frame andmouthpiece/coupling assembly taken along line 7--7 of FIG. 6;

FIG. 8 is a top plan view of the stereotactic frame andmouthpiece/coupling assembly of FIG. 6;

FIG. 9 is an enlarged top perspective view of the mouthpiece/couplingassembly of FIG. 1;

FIG. 10 is a cross-sectional view of the mouthpiece taken along line10--10 of FIG. 9;

FIG. 11 is a schematic block diagram of an interlock system used withthe stereotactic fixation apparatus of the present invention;

FIG. 12 is a flow chart which illustrates the general function of theinterlock system;

FIG. 13 is an exploded top perspective view of a calibration phantomused with the stereotactic frame of FIG. 1 in accordance with apreferred embodiment of the present invention;

FIG. 14 is a side elevational view of the calibration phantom attachedto the stereotactic frame of FIG. 13;

FIG. 15 is a rear elevational view of the calibration phantom andstereotactic frame of FIG. 14 as view in the direction of line 15--15;and

FIG. 16 is an exploded top perspective view of a stereotactic fixationapparatus in accordance with a second preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a stereotactic fixation apparatus 10 configured inaccordance with a preferred embodiment of the present invention. Thestereotactic fixation apparatus 10 is designed to immobilize a patient'sskull, and is typically used with focal radiation therapy involvingproton beam treatment. It is contemplated, however, that the presentstereotactic fixation apparatus can be used in connection with a varietyof medical diagnostic and treatment procedures.

With reference to FIG. 1, the stereotactic fixation apparatus 10principally comprises a generally flat adaptor board or platform 12supporting a stereotactic frame 14. A vacuum interface is used to securethe frame 14 to the adaptor board 12, as discussed in detail below.

A coupling or universal joint 16 extends outwardly from the frame 14 andsupports a mouthpiece 18. The universal joint 16, which connects themouthpiece 18 to the frame 14, allows a wide range of differentpositions and orientations of the mouthpiece 18 in relation to thestereotactic frame 14. Once set in a desired position, the universaljoint 16 is locked and remains attached to the mouthpiece 18 throughoutall subsequent planning and treatment phases of the patient's course. Inthis manner, the universal joint 16 forms a mechanical memory of thepatient's skull position with respect to the stereotactic frame 14.

The mouthpiece 18 includes an acrylic impression (i.e., a bite block 20formed as an impression) of the patient's upper mouth. A vacuum is usedto removably secure the mouthpiece 18 onto the hard palate and upperteeth of the patient. For this purpose, the mouthpiece 18 connects to avacuum source via a rigid tube 22, which passes through the universaljoint 16 and connects to a flexible vacuum line 24. The mouthpiece 18 isalso configured to provide a fluidic path between a port 26 to which thetube is connected and at least one hole 28 in an upper surface 30 of theacrylic impression 20. When used, a vacuum is applied between themouthpiece 18 and the patient's upper mouth to precisely position andsecure the acrylic impression 20 to the patient's dentition and hardpalate.

With reference to FIG. 2, the stereotactic fixation apparatus 10 mayalso include a patient-activated quick-release mechanism with a safetyinterlock. This quick-release mechanism includes a patient-activatedswitch 32 connected to a vacuum control system 34. The vacuum controlsystem 34 controls the application of vacuum pressure to the mouthpiece18 and to the vacuum interface between the stereotactic frame 14 and theadaptor board 12, as discussed in detail below. When the patientactivates the switch 32, the vacuum control system 34 disconnects thevacuum sources from the mouthpiece 18 and the adaptor board12/stereotactic frame 14 interface so that the patient can dislodge themouthpiece 18 from his or her mouth, as well as remove the frame 14 froma position surrounding the patient's head.

The vacuum control system 34 also electronically communicates via line36 with a medical diagnostic or treatment device (not shown in FIG. 2),such as, for example, a CAT (computer axial tomography) or MRI (magneticresonance image) scanner, or an irradiation treatment device. When thepatient activates the switch 32, the control system 34 deactivates themedical diagnostic or treatment apparatus so as not to expose non-targetsite tissue to any irradiation emitted by the diagnostic or treatmentapparatus and to prevent misalignment of the patient's head duringdiagnostic or treatment procedures which may lead to unwanted exposureof non-target site tissue to irradiation.

For purposes of describing the preferred embodiment, a coordinate systemis provided as illustrated in FIG. 1. Additionally, as used herein, "thelongitudinal direction" refers to a direction substantially parallel tothe longitudinal axis. "The lateral direction" and "the verticaldirection" are likewise in reference to the lateral axis and verticalaxis, respectively.

The individual components of the stereotactic fixation apparatus 10 willnow be described in detail with reference to FIGS. 1-10.

Adaptor Board

FIGS. 1-3 best illustrate the adaptor board 12. The adaptor board 12generally has a rectangular shape sized to support an adult body in asupine position. The adaptor board 12 desirably has a size and shapewhich is coextensive with conventional gurneys or hospital diagnosticand treatment tables. The adaptor board 12 can thus be placed onto of adiagnostic or treatment table or gurney when a medical procedure ispreformed using the present stereotactic fixation apparatus 10. It isalso contemplated that the adaptor board 12 can alternatively beintegrally formed with a dedicated diagnostic or radiation therapytreatment table or gurney.

As illustrated in FIG. 3, the adaptor board 12 may include arectangular-shaped plank 38 which cantilevers from a superior end 40 ofthe adaptor board 12. The plank 38 has a width and a length slightlylarger than that of a human skull. In an exemplary embodiment, the plank38 has a length approximately equal to 10 inches (25.4 cm) and a widthapproximately equal to 8 inches (20.3 cm). It is understood, however,that the plank 38 could have a variety of shapes and sizes, dependingupon the specific application of the stereotactic fixation apparatus 10.

The adaptor board 12, proximate to its superior end 40, defines a firstrectangular recess 42 positioned generally symmetric with a longitudinalaxis of the adaptor board 12. The recess 42 has a length that extendsfrom a point proximate to the superior end 40 into the plank 38. Therecess 42 is sized to receive a portion of a headrest 44 (see FIG. 3),which supports the patient's head and neck during the medical procedure.

The adaptor board-12 additionally includes a second rectangular recess43 also positioned generally symmetrically with the longitudinal axis ofthe adaptor board 12. The second recess 43 is located below the firstrecess 42, and has a shape and size substantially identical to those ofthe first recess 43.

As illustrated in FIG. 3, the headrest 44 used with the adaptor board orplatform 12 has an arcuate upper surface 46 which cradles the patient'sskull and the nape of the patient's neck. A base 48 of the headrest 44has a rectangular shape of a width and length generally equal to thoseof the recesses 42, 43 so as to be snugly received by recesses 42, 43.

The headrest 44 may be formed of any of a wide variety of material ofsufficient rigidity and integrity to support the patient's head andneck. In an exemplary embodiment, the headrest 44 is vacuum-formedplastic. However, those skilled in the art will realize that theheadrest 44 can be formed of a variety of different materials by avariety of different methods, known or developed in the art.

With reference to FIG. 3, the adaptor board 12 defines a series ofpaired stations 50 which interface with corresponding footings 52 of thestereotactic frame 14. Each station 50 includes a generallyrectangularly shaped groove 54 into which a correspondingly shapedO-ring 56 is seated. The O-ring 56 is advantageously positioned on theadaptor board 12 rather than on the corresponding footing 52 because theO-ring 56 is less likely to fall off or be displaced when positioned onthe adaptor board 12. However, it is contemplated that the O-ring couldbe secured to the frame footing 52.

The O-ring 56 desirably has a diameter larger than the depth of thecorresponding groove 54. The O-ring 56 thus extends above the surface ofthe adaptor board 12 when seated within the groove 54.

The shape and size of each O-ring 56 desirably matches the general shapeand size of the stereotactic frame footing 52. More preferably, eachO-ring 56 has a corresponding shape that is slightly smaller than theperiphery of the footing 52 such that with the footing 52 positionedover the O-ring 56, the entire O-ring 56 is compressed between theadaptor board 12 and the bottom surface of the footing 52.

With reference to FIG. 4, each station 50 also includes at least twoholes 58 sized and positioned to receive guide pins 60 of thecorresponding footing 52. These holes 58 are positioned with respect tothe O-ring 56 such that with the guide pins 58 inserted into the holes58, the footing 52 completely covers the O-ring 56. The O-ring 56 thusseals the periphery of the footing 52 at the interface between thefooting 52 and the adaptor board 12.

FIGS. 5a-5c illustrate the plurality of paired stations 50 of theadaptor table 12. The spacing between these stations 50 is set toposition the stereotactic frame 14 either proximate to the patient'sshoulders or proximate to the superior portion of the patient's head.The variety of positions of the stereotactic frame 14 on the adaptorboard 12 permits the present stereotactic fixation apparatus 10 to beused in radiotherapy procedures where the target is located above thebase of the skull or in those procedures where the target is locatedbelow the base of the skull.

Stereotactic Frame

With reference to FIG. 3, the stereotactic frame 14 generally has aninverted "U" shape formed by two vertical legs 62 interconnected by anupper horizontal leg 64. The stereotactic frame 14 desirably has asufficient lateral width and vertical height to surround the skull ofthe patient.

Each vertical leg 62 terminates in a footing 52. As discussed above, thefootings 52 rest flush against the top surface of the adaptor board 12.

As best seen in FIGS. 6 and 7, the horizontal leg 64 of the stereotacticframe 14 includes a tang 66 to which the universal joint 16 is attached.The tang 66 extends from the horizontal leg 64 toward the adaptor base12, and, as best seen in FIG. 7, has a "V" shape. With reference to FIG.6, the tang 66 extends from the horizontal leg 64 at an asymmetricposition with respect to the vertical legs 62. This asymmetric positionis selected to symmetrically position the mouthpiece 18 between thevertical legs 62 when the coupling 16 is attached to the tang 68, asbest seen in FIG. 6.

The horizontal leg 64 also includes a bore 68 that extends in thevertical direction through the horizontal leg 64. An axis of the bore 68is desirably aligned with the center line of the V-shaped tang 70.

The stereotactic frame 14 also includes a plurality of pins 70positioned on the vertical and horizontal legs 62, 64. The pins 70 areused to support a stereotactic reference phantom (not shown), which isused to align the stereotactic target with the isocenter of thetreatment machine, as discussed more fully in the article "Research inImmobilization and Repeatable Positioning," Proton Treatment CenterNewsletter, vol. 2, no. 4, Oct. 1992, which is incorporated by referenceherein.

With reference to FIG. 4, each footing 52 has a generally rectangularblock shape. A recess 72 extends into the footing 52 from a bottomsurface 74. The footing 52 also includes a channel 76 that extends fromthe recess 72 to an effluent port 78, desirably positioned on the outerlateral side of the footing 52. It should be noted, however, that arecess, channel and port could alternatively be formed in the adaptorboard 12.

The effluent port 78 is formed by a threaded counterbore 80, whichcircumscribes the channel 76. A conventional tube fitting 82 is threadedinto the threaded bore 80 to complete the port 78.

A vacuum tube 84 is attached to the fitting 82 to interconnect thevacuum tube 84 to the footing 52 and to place the recess 72 in fluidiccommunication with the vacuum tube 84.

As noted above, each footing 52 includes at least two guide pins 60 thatextend downwardly from a bottom surface 86 of the recess 82. The guidepins 60 are advantageously positioned in reference to the periphery ofthe recess 72 so as to position the recess 72 within the circumferenceof the O-ring 56 when the guide pins 60 are inserted into thecorresponding holes 58 in the adaptor board 12.

Universal Joint

With reference to FIG. 9, the universal joint 16 is desirably formed bya plurality of adjacent discs. In an exemplary embodiment the universaljoint 16 includes three adjacent discs 88, 90, 92. The axes of the discs88, 90, 92 are collinear. A bore 94, concentrically positioned about theaxis of the disc 88, 90, 92, extends through the disc assembly.

A fastener 96, such as a nut 98 and bolt 100, is used to join the discs88, 90, 92 together. The bolt 98 passes through the bore 94. The nut 96threads onto the bolt 98 from the opposite side to secure the bolt 98within the bore 94.

The first end disc 88 includes a first bore 102 that passes through thefirst end disc 88 in a direction generally normal to the axis of thecentral bore 94. The first bore 102 is also offset from the center ofthe disc 88 so as not to intersect with the central bore 94. Thus, thefirst bore 102 extends along an arc length of the first end disc 88,rather than along a diameter of the first end disc 88. So positioned, asmall arc length of the first bore 102 is truncated. That is, the firstbore 102 breaks through a lateral side surface (not shown) of the disc88. The corresponding truncated arc length is desirably less than 30°,and more preferably equal to about 10°.

The first bore 102 receives the generally rigid tube 22, which in turnis attached to the mouthpiece 18 via the tube fitting 26 positioned onan anterior end 108 of the mouthpiece 18. The tube 22 has a diameterslightly smaller than that of the first bore 102 so that the tube can berotated within the bore 102.

With the tube 22 inserted through the first bore 102, a small portion ofthe tube's external surface extends beyond the flat lateral side surfaceof the first end disc 88 and lightly contacts the opposing flat lateralsurface of the center disc 90. When the fastener 96 is loosened, thetube 22 can rotate relative to the first end disc 88, and the first enddisc 88 can rotate relative to the center disc 90. When the fastener 96is tightened, however, the frictional contact between the first end disc88 and the center disc 90 prevents the first end disc 88 from rotatingrelative to the center disc 90. Likewise, the frictional contact betweenthe center disc 90 and the exterior portion of the tube 22 that extendsbeyond the lateral side surface of the first end disc 88 prevents thetube 22 from rotating within the first bore 102 of the first end disc88.

The universal joint 16 also includes a mounting rod 110 that extends inthe longitudinal direction, normal to the common axis of the discassembly. The rod 110 extends through a second bore 112. The second borepasses through the central disc 90 and a second end disc 92 at theinterface of the central disc 90 and the second end disc 92. The secondbore 112 is also offset from the center of the discs 90, 92 so as not tointersect with the central bore 94. Thus, the second bore 112 extendsalong an arc length of the discs 90, 92, rather than along a diameter ofthe discs 90, 92.

The rod 110 is inserted through the second bore 112 and is capturedbetween the center disc 90 and the second end disc 92. Thisconfiguration allows the universal joint 16 to be rotated about the rod110 when the fastener 96 is loosened. When the fastener 96 is tightened,the central disc 90 and the second end disc 92 clamp against the rod 110to prevent rotation of the disc assembly about the rod 110.

With reference to FIG. 9, one end of the support rod 110 connects to amount block 114. The mount block 114 has a generally rectangularblock-like shape with a V-shaped notch 116 formed on an upper end. Theshape of the V-notch 116 desirably matches that of the V-shaped tang 66on the stereotactic frame 14. The mount block 114 also includes athreaded bore 118 that extends in the vertical direction through theblock 114. The axis of the bore 118 substantially coincides with acenter line of the block 114 in the vertical direction.

As discussed below, the mounting block 114 is attached to the horizontalleg 64 of the stereotactic frame 14, and is positioned thereon byinserting the V-shaped tang 66 into the correspondingly V-shaped notch116 of the mount block 114. With reference to FIG. 7, an elongatedthreaded shaft 120 of the knob 122 is inserted through the bore 68 andengages the threaded bore 118 of the mount block 114. In this manner,the universal joint 16 is secured to the stereotactic frame 14.

Mouthpiece

With reference to FIGS. 9 and 10, the mouthpiece 18 includes the acrylicimpression 20 attached to an impression tray 124. The mouthpiece 18generally has a U-shape that corresponds to the shape of the patient'supper dentition.

FIG. 10 illustrates a cross section of the mouthpiece 18. The acrylicimpression 20 has an upper surface 30 that is, as noted above, areproduction of an impression of the patient's dentition and hardpalate. The acrylic impression 20 includes a skirt 128, which extendsupwardly and surrounds the circumference of the U-shaped acrylicimpression 20 so as to extend over the outer surfaces of the patient'supper teeth and the poster border of the hard palate when inserted inthe patient's mouth.

A hollow 130 is formed inside the acrylic impression 20. The aperture 28is formed between the inner surface of the hollow 130 and the uppersurface 30 of the acrylic impression 20. The aperture 28 places thehollow 130 in fluidic communication with the upper surface 30 of theacrylic impression 20. A flat bottom surface 132 circumscribes thehollow 130, as well as extends around the periphery of the acrylicimpression 20.

The acrylic impression 20 is formed by first taking an impression of thepatient's dentition and upper palate. A putty-like material, such as,for example, algenate or silicon, is spread into a conventional dentaltray. The dental tray is then placed in the patient's mouth and ispushed upwardly against the upper teeth and hard palate to take animpression. The material desirably hardens within a short period of time(e.g., 90 seconds). The hardened impression is then removed from thepatient's mouth.

A study cast is made of the patient's dentition and hard palate usingthe dental impression. A study cast, as known in the art, is apermanent, exact reproduction of the patient's upper dentition and roofof mouth.

The cast, in turn, becomes the basis for the acrylic impression itself.The acrylic impression 20 is formed by sputtering a layer of self-curingorthodontic resin over the study cast. This process is repeated severaltimes until the acrylic impression 20 has a desired thickness. Theacrylic impression 20 advantageously has a sufficient thickness toprovide the necessary structural integrity such that the acrylicimpression 20 does not crack or break during use. In an exemplaryembodiment, the acrylic impression 20 has a thickness equal to about 1/8inch (0.3 cm). It is contemplated, however, that the acrylic impression20 can have a thickness of any of a variety of sizes depending upon theparticular application of the acrylic impression 20. The acrylicimpression 20 is then attached to the impression tray 124 using amoldable orthodontic resin, such as TRIAD®-VLC resin, which is curedwith visible light.

With the acrylic impression 20 attached to the study cast, the sealingskirt 128 is put around the circumference of the acrylic impression 20and molded to the outer surface of the upper teeth and the postercircumference of the hard palate. A silicon-based impression material,such as, for example, Extride®-Kerr Polyvinylsiloxane, is preferablyused to form the seal 120.

Formed from the study cast, the acrylic impression 20 reproduces theimpression, not only of the patient's teeth (or alveolar ridge, if thepatient is edentulous) but also the entire surface of the hard palate.

The hole 28 is then placed in the upper surface 30 of the acrylicimpression 20 to form a passageway from the upper surface 30 into thehollow 130 inside the acrylic impression 20.

A normally closed, one-directional flow valve 131 may be used with theacrylic impression 20 as an added safeguard to prevent the patent fromdislodging the mouthpiece 18. With reference to FIG. 10, the valve 131includes a valve body 133 with a central channel 135 passingtherethrough. The channel 135 of the valve 131 desirably has a diametermatching that of the hole 28 in the acrylic impression upper surface 30.

The valve 131 further includes a valve membrane 141 formed of an elasticmaterial with sufficient structural integrity to normally close thechannel 135 of the valve 131, yet open slightly when the pressure in thehollow 130 of the acrylic impression 20 is less than the pressure in thechannel 135. The elastic material preferably comprises a silicon sheet;however, it is understood that any of a wide variety of materials may beused as well. The valve membrane 141 is fixed to the valve body 133 attwo points located on opposite sides of the channel 135.

A second end 143 of the valve is attached to the inner surface of thehollow 130 of the acrylic impression 20 by an epoxy adhesive. Desirably,the hole 28 in the upper surface 30 of the acrylic impression 20 and thechannel 135 of the valve 131 are aligned.

The volume within the valve body 133 desirably is substantially less(e.g., 10% or less) than the volume within the hollow 130 of the acrylicimpression 20.

As illustrated in FIG. 10, the impression tray 124 includes a generallyflat platform 134 having a size and shape generally coextensive withthat of the acrylic impression bottom surface 132. The platform 134includes a recess 136 positioned within the circumferential edges of theplatform 134.

As best seen in FIG. 7, the impression tray 124 desirably has a minimalprofile to minimize the invasiveness of the impression tray 124 wheninserted in the patient's mouth. In the exemplary embodiment, themaximum thickness of the impression tray 124 is about 0.5 inch (1.3 cm);however, those skilled in the art will readily appreciate that theimpression tray 124 could be formed of a wide variety of sizes,depending upon the specific application of the mouthpiece 18. In anexemplary embodiment, as illustrated in FIG. 10, the impression tray 124has a generally triangular cross-sectional shape. This shape reduces theobtrusiveness of the mouthpiece 18 when worn by the patient, as thewidth of the mouthpiece 18 is reduced towards the back of the patient'spalate so as to fit more comfortably within the patient's mouth.

FIG. 10 illustrates an internal channel 138 formed between the anteriorend 108 of the impression tray 124 and the platform recess 136. Thechannel 138 preferably has a circular cross-sectional shape equal tothat of the inner lumen of the tube 22. The channel 138 extends normalto both the platform surface 134 and to the anterior end 108 of theimpression tray 124 and includes a 90° bend between these two sectionsof the channel 138. The wall of the channel 138 may include a chamfer140 at the 90° bend to improve fluidic flow through the channel 138, asknown in the art.

The anterior end 108 of the impression tray 124 also includes acounterbore 142 that circumscribes the channel 138. The counterbore 142,as illustrated in FIG. 10, receives the conventional tube fitting 26 toattach the tube 22 to the impression tray 124, with the inner lumen ofthe tube 22 communicating with the channel 138 of the impression tray124. The fitting 26 desirably has a diameter substantially equal to orless than the width of the impression tray 124 at its anterior end 108such that the fitting 26 sits flush against the anterior end 108 of theimpression tray 124.

When the acrylic impression 20 is mounted to the tray 124, a fluidicpath is formed from the port 26 of the tray 124, through the channel138, into the hollow 130 of the acrylic impression 20, and through thehole 28 in the upper surface 30 of the acrylic impression 20.

Patient-Activated Quick-Release Mechanism

As discussed above, the stereotactic fixation apparatus 10 may alsoinclude a patient-activated quick-release mechanism. With reference toFIG. 2, the patient-activated switch 32 communicates with the vacuumcontrol system 34. The vacuum control system 34 controls the applicationof vacuum pressure to the mouthpiece 18 and to the interface regionbetween the stereotactic frame 14 and adaptor board 12. In an exemplaryembodiment, the vacuum control system includes at least two solenoidvalves (not shown) which are positioned between the vacuum source andthe ports 78, 26 of the stereotactic frame footings 52 and themouthpiece 18, respectively. When the stereotactic frame 14 is attachedto a patient's skull, the vacuum control system 34 holds the solenoidvalves open such that a vacuum is drawn in the mouthpiece 18 and at theinterface between the stereotactic frame 14 and the adaptor board 12. Inthis manner, the mouthpiece 18 is drawn against the patient's hardpalate, and the vacuum created between the footings 52 of thestereotactic frame 14 and the adaptor board 12 holds the stereotacticframe 14 against the adaptor board 12.

If the patient activates the switch 32, the vacuum control system 34closes the solenoid valves to disconnect the vacuum source from thefootings 52 of the stereotactic frame 14 and from the mouthpiece 18. Thepatient may then dislodge the mouthpiece 18 from his or her mouth andremove the frame 14 from the position surrounding the patient's head. Inthis manner, the patient can quickly remove the stereotactic frame andmouthpiece if the patient chokes, vomits, or otherwise experiencestrouble breathing.

As discussed above, the vacuum control system 34 also can communicatewith the medical diagnostic or treatment device (not shown) used inconjunction with the stereotactic fixation apparatus 10. FIG. 11schematically represents an interlock subsystem 150 of the controlsystem 34 which enables and disables the medical treatment device 152(e.g., a proton beam emitter).

As seen in FIG. 11, the interlock system 150 includes several sensors154, 156, such as, for example, vacuum switches, located at theframe/platform interface regions 72, and in or proximate to themouthpiece 18, respectively. The sensors 154, 156 detect the applicationof a vacuum and generate a signal which indicates the presence orabsence of a vacuum at the corresponding location. The interlock system150 also may include a presence detect sensor 158, e.g., amicro-switch(es), which the stereotactic frame 14 activates whenpositioned over one of the pairings of stations 50 on the platform 12.

The interlock system 150 also includes logic 160 which selectivelygenerates an enable signal depending upon the presence or absence ofvacuum at the mouthpiece 18 and at the frame/platform interface region72, and depending upon whether the patient has actuated the hand heldsafety switch 32. For this purpose, the logic 160 receives input signalsfrom the frame interface vacuum sensors 154, the mouthpiece vacuumsensor 156, the presence detect sensor 158, and the patient switch 32,and interprets the signals to determine whether to generate an enablesignal. The logic 160 may include hard wired logic circuitry, includingcomparators and/or relays, or a microprocessor based platform, includingmemory, programmed to execute the desired function.

FIG. 12 is a flow chart illustrating the general function performed bythe logic 160. It should be understood that the function can beperformed in any of a variety of sequences.

As represented in decision block 162, the logic 160 determines whetherthe mouthpiece 18 is in use or whether another fixation apparatus isbeing used with the system (such as, for example, the immobilizationmask described below). In the illustrated embodiment, the logic 160determines whether the input signal for the micro-switch 158 indicatesthat the footings of the stereotactic frame 52 have been positioned overthe corresponding stations 50 of the platform 12.

If the mouthpiece and corresponding stereotactic frame 14 are in use,the logic 160 determines whether the vacuum switch 156 on the mouthpiece18 is activated, which indicates the presences of a vacuum, as discussedabove. Decision block 164 of FIG. 12 represents this function. For thispurpose, the logic 160 examines the signal from the vacuum switch 158.

If the mouthpiece 18 is not in use (decision block 162), the logic 160skips the determination of whether the mouthpiece vacuum switch 158 isactivated (i.e., skips decision block 164).

As represented in decision block 166, the logic 160 also determineswhether the patient's hand held switch 32 is unactuated by examining thecorresponding input signal. If unactuated, the logic 160 proceeds withits function.

The logic further determines whether the vacuum switch 154 at theplatform/frame interface region 72 is activated, which indicates thepresences of a vacuum, as discussed above. Discission block 168represents this function. For this purpose, the logic 160 examines theinput signal from the corresponding vacuum switch(es) 154.

If all of the vacuum switches 154, 156 are actuated and the patient'semergency switch 32 remains unactuated, the logic 160 generates anenable signal, as represented in operation block 170.

As schematically illustrated in FIG. 11, a selection verification system172 receives the enable signal from the logic 160 of the interlocksystem 100 via the transmission line 36. If the treatment device 152(i.e., beam emitter) is otherwise configured correctly, as determined bythe selection verification system 172, and a treatment beam has beenrequested, the selection verification system 172 activates treatmentdevice 152. A suitable selection verification system 172 is disclosed inU.S. Pat. No. 5,260,581, issued Nov. 9, 1993, which is herebyincorporated by reference.

If, however, any one of the vacuum switches 154, 156 is not activated(see decision blocks 164,168 of FIG. 12), or if the patient switch 32 isactivated (see decision block 166), the logic 160 does not generate anenable signal, as represented in operation block 174. The selectionverification system 172 (FIG. 11) advantageously cannot operate thetreatment device 152 without receiving an enable signal from theinterlock system 100.

Thus, for instance, when the patient activates the safety switch 32, thecontrol system 34 interrupts the enable signal to disable the medicaldevice 152. Any radiation emitted by the medical device 152 immediatelyceases so as not to expose non-targeted tissue to irradiation. Thus, thepatient can dislodge and remove the restraints of the mouthpiece 18 andstereotactic frame 14 without the danger of unintentional irradiation.

Calibration Phantom

With reference to FIG. 13, a calibration phantom 176 may be used withthe above-described stereotactic fixation apparatus 10 to calibrate oralign reference planes between diagnostic equipment (e.g., CAT or MRIscanners) and treatment equipment (e.g., a rotatable proton beamgantry). That is, the calibration phantom 176 provides a way forreplicating the exact position of the patient's skull relative to thescanning plane of a medical diagnostic device throughout all subsequenttreatment phases of the patient's course, as described more fully below.

The calibration phantom 176 attaches to a point on the stereotacticframe 14 or like support to which the detachable fixation deviceattaches. In the illustrated embodiment, the calibration phantom 176attaches to the v-shape tang 66. Because the mouthpiece 18 is attachedto the frame 14 only at one specific point (i.e., at the tang 66), onlythe orientation between that point and the scanning plane needs to bereplicated in subsequent procedures. The relative orientation betweenthe rest of the frame 14 and/or platform 16 and the scanning plane isirrelevant.

As seen in FIG. 13, the calibration phantom 176 includes a plurality ofmarkers 178 arranged so as to lie in a single plane. The markers 178also are arranged so as to define at least two intersecting axes. Theaxes preferably are perpendicular to each other. One of the defined axesdesirably lies generally parallel to the platform and the other axisdesirably lies generally perpendicular to the platform. In use, asdiscussed below, the defined axes are aligned with the reference axes ofthe scanning plane of the diagnostic equipment.

A plurality of posts 180 of equal length desirably support the markers178 on a flat plate 182 in the desired arrangement. Each post 180supports one marker 178.

In the illustrated embodiment, the calibration phantom 176 includes fourmarkers 178. The posts 180, which support the markers 178, are locatedabout at the corners of the plate 182, which has a generally squareshape. Ribs 184 connect the posts 180 together, generally about theperiphery of and diagonally across the plate 182, to strengthen theplate 182 and to interconnect the posts 180.

The markers 178 comprise spherical balls made of a material which isopaque to at least some wavelengths of electromagnetic energy. Themarkers 178 desirably are made of a material which is easily visible onx-ray and computer tomography (CT) images, such as, for example,ceramic. The markers 178 preferably have a diameter of 3 mm. The spacingbetween the horizontal set of markers 178 equal about 25 cm (9.84inches). The spacing between the vertical set of markers 178 equalsabout the same. It is understood, however, that the size of the markers178 and the spacing between the markers 178 could be varied to suit theparticular requirements of a specific application.

With reference to FIG. 13, a universal joint 16a, similar to thatdescribed above, supports the plate 182 on the stereotactic frame 14.Where appropriate, like reference numerals with an "a" suffix have beenused to indicate like component between the universal joint 16 used withthe mouthpiece 18 and the universal joint 16a used with the calibrationphantom 176 for ease of understanding. It also is understood that thepresent universal joint 16a is configured in accordance with the generaldescription of the universal joint 16 above, except where indicatedotherwise.

The universal joint 16a includes a support rod 110a, one end of which isconnected to a mount block 114a. The mount block 114a has a generallyrectangular block-like shape with a v-shaped notch 116a formed on anupper side. The shape of the notch 116a matches that of the v-shapedtang 66 on the stereotactic frame 14. The mount block 116a also includesa threaded bore 118a to attached the block 116a to the stereotacticframe 14 in a manner similar to that explained above in connection withthe universal joint 16 connected to the mouthpiece 18.

In the illustrated embodiment, the universal joint 16a also includes aplurality of adjacent discs 88a, 90a, 92a with a fastener 96a passingthrough a common central bore 94a of the adjacent discs 88a, 90a, 92a.The fastener 96a joins the discs 88a, 90a, 92a together to form a discassembly. The fastener 96a can be tightened or loosened so as to movethe fastener 96a from an expanded position, in which the discs 88a, 90a,92a can be rotated relative to one another, to a contracted position, inwhich the discs 88a, 90a, 92a are locked in a set position.

The mounting rod 110a passes a bore 112a that extends through thecentral disc 90a and the second end disc 92a, similar to the universaljoint 16 described above. The discs 90a, 92a capture the rod 110a suchthat the disc assembly can be rotated about the rod 110a when thefastener 96a is loosened. When the fastener 96a is tightened, thecentral disc 90a and the second end disc 92a clamp against the rod 110ato prevent rotation of the disc assembly about the rod 110a.

The disc assembly also includes another bore 102a that passes throughthe first end disc 88a in a direction generally normal to the axis ofthe central bore 94a. The bore 102a is also offset from the center ofthe disc 88a so as not to intersect with the central bore 94a. In thisoffset position, a small portion of the bore 102a breaks through thelateral side surface (not shown) of the first disc 88a. The arc of thisportion has an angle desirably less than 30°, and more preferably aboutequal to 10°.

As best seen in FIGS. 14 and 15, the bore 102a between the first disc88a and the center disc 90a receives a mounting rod 186 attached to theplate 182. The mounting rod 186 has a diameter slightly smaller than thebore 102a so that it can be rotated within the bore 102a. With themounting rod 186 inserted through the bore 102a, a small portion of therod 186 extends beyond the flat lateral side surface of the first enddisc 88a and lightly contacts the opposing flat lateral surface of thecenter discs 90a. When the fastener 96a is loosened, the base plate 182and the mounting rod 186 can rotate relative to the disc assembly, andthe first end disc 88a and mounting rod 186 can rotate relative to thecenter disc 90a. When the fastener 96a is tightened, however, thefrictional contact between the first end disc 88a and the center disc90a prevents the first end disc 88a from rotating relative to the centerdisc 90a. Likewise, the frictional contact between the center disc 90aand the portion of the mounting rod 186 that extends beyond the lateralside surface of the first end disc 88a prevents the rod 186 fromrotating within the bore 102a of the first end disc 88a.

With reference to FIGS. 13 and 14, a pair of support blocks 188 suspendthe mounting rod 186 at a position distanced from the base plate 182.The mounting rod 186 lies substantially parallel to the plane defined bymarkers 178 of the calibration phantom.

In the illustrated embodiment, the support blocks 188 are mounted on aside of the base plate 182 opposite of the side on which the markers 178are located. The blocks 188 desirably support the mounting rod 186 suchthat the rod extends in a direction which is generally parallel to theaxis defined between the vertical pairing of markers 178. The supportblocks 188 also are arranged on the plate 182 so as not to interferewith the universal joint 16a, which supports the plate 182, as the plate182 is moved to align the markers 178 with the corresponding scanningplane axes, as described below.

As best seen in FIG. 15, the base plate 182 includes an opening 190which passes though the plate 182 at a location adjacent to the mountingrod 186. In this position, the opening 190 provides a relief throughwhich the support rod 110a of the universal joint passes.

The base plate 182, support posts 180, ribs 184, support blocks 188 andmounting rod 186 desirably are all formed of a material which isgenerally transparent to the electromagnetic energy used with theparticular imaging process, such as, for example, x-ray, CAT, CT or MRI.In an exemplary embodiment, these components are formed of acrylic orlike thermoplastic, and are joined together with a suitable bondingagent, such as, for example, methylethylketone (MKE).

Method of Use

When using the stereotactic fixation apparatus 10, a patient lies on theadaptor board 12 in a supine position. The headrest 44 is placed withinthe recess 42 or 43 on the board 12, and the patient is positioned suchthat the headrest 44 cradles the posterior side of the patient's skulland supports the nape of the patient's neck.

The stereotactic frame 14 is then placed over the patient and ispositioned at a desired location relative to the patient's skull.Specifically, the guide pins 60 of the stereotactic frame 14 areinserted into the hole 58 of the adaptor board 12 at the desiredlocation. The footings 52 of the stereotactic frame 14 sit on top of theadaptor board 12 and compress the O-rings 56 to seal the cavities formedby the recesses 72 of the footings 52 and the top surface of the adaptorboard 12. A vacuum supply line 84 (FIG. 2) is connected to the fitting82 of each footing 52. A vacuum source is then activated to produce avacuum within the cavity so as to draw the footing 52 against theadaptor board 12. In this manner, the stereotactic frame 14 is removablysecured to the adaptor board 12.

The universal joint 16 is attached to the stereotactic frame 14 byinserting the V-shaped groove 116 of the mount block 114 over theV-shaped tang 66 that extends below the horizontal leg 64 of thestereotactic frame 14. When the surfaces of the tang 66 and groove 116are in contact, the knob 122 is turned to screw the rod 124 attached tothe knob 122 into the threaded bore 118 of the mount block 114. The knob122 is tightened until the mount block 114 is drawn tightly against thetang 66. A set screw or like locking mechanism inserted through anaperture 152 (see FIGS. 6 and 7) in the horizontal leg 64 of thestereotactic frame 14 may be used to lock the rod 124 in place while themount block 114 is aligned to the tang 66.

As noted above, the universal joint 16 provides the mouthpiece 18 withthree degrees rotational freedom in relation to the stereotactic frame14. The longitudinal distance between the mouthpiece 18 and thestereotactic frame 14 can also be adjusted by sliding the universaljoint 16 along the rod 110. The vertical position of the mouthpiece 18relative to the stereotactic frame 14 can also be adjusted by slidingthe rigid tube 22 through the first bore 102 in the desired direction.In this manner, the mouthpiece 18 can be adjusted relative to the frame14 during the stereotactic localization procedure.

A vacuum is then applied to the mouthpiece 18 through the port 26 vialine 24. The vacuum line 24 is preferably connected to a suctioncanister 154 (see FIG. 2) which receives any saliva drawn from thepatient's mouth, as known in the art.

Vacuum pressure is thus applied to the hard palate through the hole 28in the upper surface 30 of the acrylic impression 20. The vacuum holdsthe acrylic impression 20 firmly against the patient's palate and causesthe acrylic impression 20 to precisely locate against the patient'sdentition and palate.

The highly accurate dental-palatal reproduction and the vacuum thusemplaces and secures the acrylic impression 20 in the same position inthe patient's mouth for each diagnostic procedure and subsequenttreatments. Because the skull is rigidly connected to the upperdentition and alveolar ridge, the repeatable positioning of the acrylicimpression 20 enables one to repeatedly position the patient's head.

The orientation of the mouthpiece is adjusted with the stereotacticfixation apparatus configured in accordance with the above descriptionand the mouthpiece 18 secured in the patient's mount by the appliedvacuum. Through the range of rotational and linear adjustment providedby the universal joint 16, the patient's skull can be adjust to rest ina comfortable position. The universal joint 16 is then locked to form amechanical memory of the patient's skull relative to the attachmentpoint (i.e., the v-shape tang 66) on the stereotactic frame 16.

As noted above, the present stereotactic fixation apparatus includes aquick release mechanism which enables the patient to quickly dislodgethe restraint of the stereotactic frame 14 and mouthpiece 18 in exigentcircumstances (e.g., choking, vomiting, etc.). The patient simplypresses the switch 32 in such exigent circumstances and sits upright.The patient can then dislodge the mouthpiece 18 from his or her mouth.As discussed above, the vacuum control system 34 disconnects the sourceof vacuum from the mouthpiece port 26 and the ports 76 of thestereotactic frame 14. The patient can then overcome the residual vacuumpressure by normal movement.

The interlock subsystem 150 of the central system 34 detects theactivation of the patient's switch 32 and disables the associatedmedical device. Imaging or treatment of the patient stops. The interlocksystem 150 thus prevents exposure of non-target site tissue to anyradiation emitted by the diagnostic or treatment apparatus. As notedabove, the interlock subsystem 150 also detects the absence of vacuumhold-down pressure at the frame/platform interfaced 72 or at the acrylicimpression 20. The interlock subsystem 150 likewise will disable theassociated treatment or diagnostic device if it defects an absence of avacuum at either of these locations.

As noted above, the orientation of the scanning plane of the medicaldiagnostic or treatment equipment relative to the mouthpiece 18desirably is consistent throughout all planing and treatment phases ofthe patient's course, even though all phases may not be performed usingthe same equipment, nor performed at the same facility. The preciseorientation between the mouthpiece 18 and the scanning plane enablesexact replicate of the position of the patient's skull relative to thescanning plane.

The mouthpiece 18 and attached universal joint 16 will accompany thepatient throughout all planning and treatment phases of the patient'scourse after the initial planning session in which the orientation ofthe mouthpiece 18 is established. This ensures that there is novariation in this apparatus from facility to facility. It iscontemplated, however, that the platform 12 and stereotactic frame 14will not. The stereotactic frame 14 and platform 12 remain with theparticular medical diagnostic or treatment equipment.

In all subsequent treatment procedures, the orientation of the supportapparatus (e.g., the stereotactic frame 14) relative to a correspondingreference plane must be calibrated with the orientation of the supportapparatus (e.g., stereotactic frame 14) used in the initial planningsecession relating to the "primary" scanning plane in order to preciselyreplicate the planned position of the patient's skull in stereotacticspace. In the illustrated embodiment, the position of the V-shaped tang66 relative to the corresponding treatment reference plane must becalibrated with the orientation of the tang 66 used in the initialplanning stage with relative to the primary scanning plane.

As noted above, the calibration phantom 176 can be used to calibrate theorientation of a skull immobilization device (e.g., the mouthpiece 18)in subsequent procedures. The calibration phantom 176 initially is fixedto the support apparatus used with the initial diagnostic equipment(e.g., a MRI or CT scanner). In the illustrated embodiment, theuniversal joint 16a is attached to the stereotactic frame 14 byinserting the V-shaped groove 116a of the mount block 114a over theV-shaped tang 66 that extends below the horizontal leg 64 of thestereotactic frame 14. When the surfaces of the tang 66 and groove 116aare in contact, the knob 122 is turned to screw the rod 124 attached tothe knob 122 into the threaded bore 118a of the mount block 114. Theknob 122 is tightened until the mount block 114a is drawn tightlyagainst the tang 66. A set screw or like locking mechanism insertedthrough an aperture 152 (see FIGS. 6 and 7) in the horizontal leg 64 ofthe stereotactic frame 14 may be used to lock the rod 124 in place whilethe mount block 114a is aligned to the tang 66.

The calibration phantom 176 is aligned with the reference axes of thescanning plane of the diagnostic equipment. Where the initial planningsecession involves computer tomography (CT) imaging, the CT deviceproduces an image of the calibration phantom markers 178 on its visualdisplay. The CT device also projects reference axes over the image ofthe calibration phantom 176. A technician rotates the plate 182 of thecalibration phantom 176 with the universal joint 16a loosened until allmarkers 178 appear in one scanning plane and are parallel with the primereference axes of the CT device. The technician locks the universaljoint 16a once the markers 176 are aligned with the CT reference axes toform a mechanical memory of the orientation of the tang 66 relative tothe CT scanning plane.

The calibration phantom 176 later is transported to a treatment room toorient the support apparatus used with the treatment device so as toreplicate the exact orientation between the support apparatus and theplanar axes of the treatment device that existed between the supportapparatus and the primary planar axes of the diagnostic device duringthe initial planning procedure.

The calibration phantom 176 is attached to the support apparatus usedwith the treatment device in a manner similar to that described above.An imaging device (i.e., x-ray machine) used with the treatment device(e.g., a rotatable proton beam gantry) is used to produce an image ofthe calibration phantom 176 attached to the support apparatus (e.g., thestereotactic frame 14). The imaging device also projects reference axesover the image of the calibration phantom 176. Images desirably aretaken from orthogonal directions.

A technician adjusts the support apparatus in response to the images toalign the markers 178 of the calibration phantom 176 with the referenceaxes of the treatment device. In the illustrated embodiment, thetechnician can shim the platform 12 in order to move the tang 66 of thestereotactic frame 14 until the markers 178 align with the referenceaxes of the treatment device.

Use of the calibration phantom 176 in the above described manner ensuresthat the location of the attachment point on the support apparatus(e.g., the tang 66 on the stereotactic frame 14) relative to thescanning plane axes is consistent with each piece of medical equipmentused throughout the patient's course. As such, the orientation of thestereotactic fixation device (e.g., the mouthpiece 18), which attachesto the support apparatus attachment point (e.g., the tang) relative tothe treatment reference axes remains constant from procedure toprocedure. In this manner, the present stereotactic fixation system canbe used to precisely and reproducible position the patient's skullthroughout all diagnostic, planning and treatment stages, even when suchprocedures are performed at different facilities.

Additional Embodiment

With reference to FIG. 16, there is provided an additional fixationapparatus 200 configured in accordance with another preferred embodimentof the present invention. The fixation apparatus 200 includes a facialmask 202 formed of a thermoplastic material. The thermoplastic materialis heated to a degree in which the material is pliable, and is thenplaced over the anterior portion of the patient's skull. The material ismolded to the contours of the patient's anterior features and is allowedto harden in this configuration. In this manner, the facial mask 202forms an impression of the patient's facial features.

The facial mask 202 is attached to a mounting frame 204 by conventionalmeans. The mounting frame generally has a U-shape of a sufficient sizeto surround the periphery of a patient's head. The mounting frame 204also includes guide pins 206 which are used to position the mountingframe 204, as discussed below.

The fixation apparatus 200 also includes an adaptor board 208. Theadaptor board 208 generally has a rectangular shape sized to support anadult body in a supine position. The adaptor board 208 includes aU-shaped recess 210 and a groove 210 that outlines the periphery of therecess 210. The groove 212 and recess 210 are sized smaller than themounting frame 204 such that the mounting frame 204 completely coversthe groove 212 and recess 210.

The adaptor board 208 further includes a seal 214 having a circularcross-sectional shape and configured to sit within the groove 212. Theseal 214 desirably has a diameter larger than the depth of thecorresponding groove 212, such that the seal 214 extends above thesurface of the adaptor board 208 when seated within the groove 212.

The adaptor board 208 further includes alignment holes 216 whichcooperate with the guide pins 206 on the mounting frame 204. Thealignment holes 216 are positioned with respect to the recess 210 andthe groove 212 so as to position the mounting frame 204 over the seal214 and the recess 210. In this manner, a substantially sealed cavity isformed between the mounting frame 204 and adaptor board 208 when themounting frame 204 covers the recess 210.

The adaptor board 208 also includes a port 218 connected to a channel(not shown) which extends through the adaptor board 208 and opens intothe recess 210 through an aperture 220. The port 218 is adapted toconnect to a source of vacuum.

When the fixation apparatus 200 is used in radiotherapy or like medicalprocedures, the patient is placed on the adaptor board 208 in the supineposition. The face mask 202 is then placed over the patient, and thepatient's skull is oriented within the face mask 202 such that the facemask 202 sits directly against the anterior features of the patient'sskull. The guide pins 206 of the mounting frame 204 are then insertedinto the alignment holes 216 of the adaptor board 208 to properlyposition the mounting frame 204 over the recess 210. The port 218 in theadaptor board 208 is then connected to a vacuum source so as to applyvacuum pressure within the recess 210. The vacuum holds the mountingframe 204 against the adaptor board 208.

The fixation apparatus 200 may also include the patient-activated quickrelease mechanism discussed above. This quick-release mechanism allowsthe patient to disconnect the port 218 from the source of vacuum uponactivation of the switch 34 (FIG. 2). When the vacuum is disconnectedfrom the port 218, the patient can remove the mounting frame 204 fromthe adaptor board 208. It should be noted that the vacuum system willinherently have slight leaks such that a vacuum lock is not formedbetween the mounting frame 204 and the adaptor board 208. Thus, thepatient will be able to overcome any residual vacuum pressure by liftinghis or her head off of the adaptor board 208.

Although this invention has been described in terms of a certainpreferred embodiment, other embodiments apparent to those of ordinaryskill in the art are also within the scope of this invention.Accordingly, the scope of the invention is intended to be defined onlyby the claims which follow.

What is claimed is:
 1. A stereotactic fixation system for immobilizing apatient's skull during a medical procedure involving a medical device,said system comprising:a platform for supporting a portion of a patient;a stereotactic fixation apparatus contacting said platform at least atone interface region; a port adapted for connection to a source ofvacuum, said port being in fluidic communication with said interfaceregion, whereby the vacuum holds said stereotactic fixation apparatusagainst said platform when vacuum pressure is applied to said interfaceregion through said port; a first sensor positioned proximate to saidinterface region, said sensor generating a first input signal indicatingthe application or absence of a vacuum at said interface region; apatient-activated switch having at least first and second operationalstates, said switch generating a second input signal when the switch isin one of said states; and a controller which receives said first andsecond input signals from said first sensor and said patient-activatedswitch, respectively, said controller generating an output signal whensaid vacuum pressure is applied at said interface region and saidpatient-activated switch is in said first state, said output signalenabling the operation of the medical device.
 2. The stereotacticfixation system of claim 1, wherein said stereotactic fixation apparatuscomprises a mouthpiece attached to a stereotactic frame, said mouthpiecehaving a surface for contacting a patient's hard palate and a portadapted for connection to the source of vacuum, said mouthpiece portlocated on the exterior of said mouthpiece, said mouthpiece beingconfigured to provide a fluidic path between said surface and said port.3. The stereotactic fixation system of claim 2 additionally comprising asecond sensor positioned proximate to said fluidic path defined by saidmouthpiece, said second sensor generating a third input signalindicating the application or absence of a vacuum in said fluidic pathof said mouthpiece.
 4. The stereotactic fixation system of claim 1,wherein said stereotactic fixation apparatus comprises a rigid face maskmounted to a frame, said face mask having a shape with conforms to thecontours of the anterior features of the patient's skull.
 5. Thestereotactic fixation system of claim 2, wherein said controllerselectively generates a second output signal to disable the source ofvacuum applied to said port of said mouthpiece and applied to said portat said interface region in response to said second input signal of thepatient-activated switch when the switch is in said second state.
 6. Amethod of interlocking the operation of a medical device with theoperational state of a quick-release stereotactic fixation apparatusused to immobilize a patient's skull, said stereotactic fixationapparatus having a patient-activated switch, said method comprising thesteps of:sensing pressure at an interface region between a portion ofsaid stereotactic fixation apparatus and a platform which supports atleast the patient's skull; determining whether vacuum pressure isapplied at said interface region to hold said stereotactic fixationapparatus against said platform; determining whether thepatient-activated switch is in a selected state; and generating a signalwhich enables the medical device when a vacuum is applied at saidinterface region and said patient-activated switch is in said selectedstate.